Gas-assisted rapid thermal processing

ABSTRACT

A system, method and apparatus for processing a semiconductor device including a processing chamber and a heating assembly positioned within the processing chamber. The heating assembly including at least a plate defining an internal cavity configured to receive gas. The gas enters the internal cavity through a first passage at a first temperature, and exits the internal cavity at a second temperature through a second passage.

BACKGROUND

[0001] 1. Field of the Invention

[0002] This invention generally relates to semiconductor manufacturingequipment and, more particularly, to an improved method for rapidthermal processing of a semiconductor wafer.

[0003] 2. Related Art

[0004] In the semiconductor manufacturing industry, depending upon theparticular process, a semiconductor wafer may be treated at temperaturesof from about 100° C. to about 1300° C., under controlled conditions, inrather sophisticated furnaces. Commonly, these furnaces are horizontalor vertical type furnaces, which use various energy sources to heat thewafer, including radiant heaters, arc lamps, and tungsten-halogen lamps.As shown in FIG. 1, a typical horizontal or vertical type furnacerequires a time t₁ for ramping up to a particular process temperature toprocess the wafers. The ramp up rate for a typical furnace is usuallybetween 5° C./min to about 15° C./min, which makes time t₁ typically onthe order of about 1 hour. A time t₂ is required for cooling of thewafers, which is generally on the order of about 2 hours. Longprocessing times are typically unacceptable in advanced semiconductordevice manufacturing because of dopant redistribution, excessive costs,excessive exposure to temperature, and high power requirements.

[0005] In order to continue to make advancements in the development ofsemiconductor devices, especially semiconductor devices of decreaseddimensions, new processing and manufacturing techniques have beendeveloped. One such processing technique is know as Rapid ThermalProcessing (RTP), which reduces the amount of time that a semiconductordevice is exposed to high temperatures during processing. The rapidthermal processing technique, typically includes raising the temperatureof the wafer and holding it at that temperature for a time long enoughto successfully perform a fabrication process, and avoid such problemsas unwanted dopant diffusion that would otherwise occur at the highprocessing temperatures.

SUMMARY

[0006] The present invention provides an improved system, method andstructure for rapid thermal processing of a semiconductor wafer. Thepresent invention helps to improve process times so as to avoid, forexample, the creation of thermal gradients in the process chamber, whichcan cause slip and warpage of the wafer. The present invention adds asignificant conductive heat transfer component to processes which maypresently use primarily radiant heat transfer to raise the temperatureof a semiconductor wafer.

[0007] In accordance with the present invention, a gas, such as He, H₂,O₂, Ar, N₂, and gases containing He, H₂, O₂, Ar and N₂, can beintroduced into the processing chamber during processing. The gas isintroduced through at least one heatable member, such as a heatableplate that can overlay a surface of the wafer. The heatable memberincludes an internal cavity in which heat is transferred to the gas. Theheated gas exits the heatable member in the direction of the wafersurface through an outlet portion of the plate. The outlet portion caninclude a plurality of holes, which are dispersed on the plate surfaceso as to evenly distribute the heated gas across the surface of thewafer. Advantageously, the addition of the heated gas to the process canraise the temperature of the wafer much more quickly then without theuse of the gas.

[0008] These and other features and advantages of the present inventionwill be more readily apparent from the detailed description of thepreferred embodiments set forth below taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

[0009]FIG. 1 is a graph representative of typical temperature heat-upand cool-down rates for a conventional wafer processing furnace;

[0010]FIG. 2 illustrates schematically a side view of one embodiment ofa semiconductor wafer processing system in accordance with the presentinvention;

[0011]FIG. 3A is a simplified cross-sectional illustration of anembodiment of a processing chamber in accordance with the presentinvention;

[0012]FIG. 3B is a simplified illustration of a side view of a heatingassembly in accordance with the present invention;

[0013]FIG. 4A is a top view of a heatable plate including standoffs forholding a wafer in accordance with an embodiment of the presentinvention;

[0014]FIG. 4B is a cross-sectional view of the heatable plate of FIG.4A;

[0015]FIG. 5 is a simplified cross-sectional illustration of anembodiment with directional gas flow indications in accordance with thepresent invention;

[0016]FIG. 6 is a graph comparing wafer temperature as a function oftime between a wafer disposed in the process chamber of FIG. 3 withoutgas flow and a wafer disposed in the process chamber of FIG. 3 with gasflow in accordance with principles of the present invention;

[0017]FIG. 7 illustrates an alternative embodiment of the processchamber of FIG. 3 used for cooling a wafer; and

[0018]FIG. 8 illustrates yet another alternative embodiment of theprocess chamber of FIG. 3 used for cooling a wafer.

DETAILED DESCRIPTION

[0019]FIG. 2 illustrates schematically a side view of one embodiment ofa semiconductor wafer processing system 10 that establishes arepresentative environment of the present invention. Processing system10 includes a loading station 12, a transfer chamber 20 and a reactor26. A robot 22 within transfer chamber 20 rotates toward loadlock 18 andpicks up a wafer 24 from cassette 16. Reactor 26, which may also be atatmospheric pressure or under vacuum pressure, accepts wafer 24 fromrobot 22. Robot 22 then retracts its arm which carried wafer 24 and,subsequently, the processing of wafer 24 begins.

[0020] Reactor 26 may be any type of reactor which allows wafers to beloaded at wafer processing temperatures, of between about 100° C. toabout 1300° C., without adverse results. In accordance with the presentinvention, the reactor may be a hot-walled RTP reactor, such as is usedin thermal anneals. In other embodiments, the reactor may be the type ofreactor used for dopant diffusion, thermal oxidation, nitridation,chemical vapor deposition, and/or similar processes. In one embodiment,process gases, coolant, and electrical connections may be providedthrough the rear end of the reactors using interfaces 34.

[0021]FIG. 3A is a simplified cross-sectional illustration of anembodiment of a reactor 100 in accordance with the present invention.Reactor 100 may generally include a closed-end process chamber 106,which defines an interior cavity 108. Process chamber 106 may beconstructed with a substantially rectangular cross-section, having aminimal internal volume surrounding wafer 110. In one embodiment, thevolume of process chamber 106 may be no greater than about 5000 cm³,preferably less than about 3000 cm³. One result of the small volume isthat uniformity in temperature is more easily maintained. Additionally,the small process chamber volume allows reactor 100 to be made smaller,and as a result, processing system 10 may be made smaller, requiringless clean room floor space. Process chamber 106 may be made ofaluminum, quartz or other suitable material, such as silicon carbide orAl₂O₃. To conduct a process, process chamber 106 should be capable ofbeing pressurized. Typically, process chamber 106 should be able towithstand internal pressures of about 0.001 Torr to 1000 Torr,preferably between about 0.1 Torr and about 760 Torr.

[0022] Opening 104, shown at the left end of process chamber 106,provides access for the loading and unloading of wafer 110 before andafter processing. Opening 104 may be a relatively small opening, butwith a height and width large enough to accommodate a wafer of betweenabout 0.5 to 2 mm thick and up to about 300 mm (˜12 in.) in diameter,and the arm of robot 22 passing therethrough. The height of opening 104is no greater than between about 18 mm and 50 mm, and preferably, nogreater than 20 mm. The relatively small opening size helps to reduceradiation heat loss from process chamber 106, and keeps down the numberof particles entering cavity 108 to allow for easier maintenance of theisothermal temperature environment.

[0023] In one embodiment, a plurality of heating elements 114 surround atop and a bottom portion of process chamber 106. Resistive heatingelements 114 may be disposed in parallel across chamber 106 such thateach element 114 is in relative close proximity to each other element114. For example, each resistive heating element 114 may be spacedbetween about 5 mm and 50 mm apart; preferably between about 10 mm and20 mm apart. Accordingly, the close spacing of heating elements 114provides for an even heating temperature distribution across the waferpositioned in cavity 108. Resistive heating element 114 may include aresistive heating element core and a filament wire. The core is usuallymade of a ceramic material, but may be made of any high temperaturerated, non-conductive material. The filament wire is conventionallywrapped around the core to allow an optimal amount of heat energy toradiate from the element. The filament wire may be any suitableresistively heatable wire, which is made from a high mass material forincreased thermal response and high temperature stability, such as SiC,SiC coated graphite, graphite, NiCr, AlNi and other alloys. Preferably,the resistive heating filament wire is made of a combination Al—Ni—Fematerial, known commonly as Kantal A-1 or AF, available from Omega Corp.of Stamford, Conn.

[0024] A direct line voltage of between about 100 volts and about 500volts may be used to power the resistive elements. Thus, in thisembodiment no complex power transformer is needed for controlling theoutput of resistive heating elements 114.

[0025] In one embodiment, reactor 100 includes heat diffusing members118 and 120, which are positioned proximate to and typically overlayheating elements 114. Heat diffusing members 118 and 120 absorb thethermal energy output from heating elements 114 and dissipate the heatevenly within chamber 106. It should be appreciated that by heatingwafer 110 from above and below, and further by keeping the distancebetween heat diffusing members 118 and 120 small, the temperaturegradient within chamber 106 is more easily isothermally maintained. Heatdiffusing members 118 and 120 may be any suitable heat diffusingmaterial that has a sufficiently high thermal conductivity, preferablySilicon Carbide, Al₂O₃, or graphite.

[0026] As further illustrated in FIGS. 3A and 3B, in one embodiment,reactor 100 includes a heating assembly 122. Heating assembly 122includes two heatable members or top plate 124 and bottom plate 126positioned, as shown in FIG. 3, adjacent and opposed to one another. Topplate 124 is spaced apart from bottom plate 126 a distance φ whichallows wafer 110 to be placed therebetween. For example, the distance φbetween plates 124 and 126 can be between about 10 mm to about 50 mm.

[0027] Heating plates 124 and 126 of heating assembly 122 may have alarge mass relative to wafer 110, and may be fabricated from a material,such as silicon carbide, quartz, Inconel, aluminum, steel, or any othermaterial that does not react at processing temperatures with any ambientgases or with wafer 110.

[0028] Arranged on a top surface of bottom plate 126 may be wafersupports 112. In one embodiment, wafer supports 112 extend outward fromthe surface of bottom plate 126 to support wafer 110. Wafer supports 112are sized to ensure that wafer 110 is held in close proximity to bottomplate 126. For example, wafer supports 112 may each have a height ofbetween about 50 μm and about 20 mm, preferably about 2 mm to about 8mm. The present invention includes at least three wafer supports 112 toensure stability. However, the total area of contact between wafersupports 112 and wafer 110 is less than the size of the wafer.

[0029] Top and bottom plates 124 and 126 may be formed into anygeometric shape, preferably a shape which resembles that of the wafer.In one embodiment, plates 124 and 126 are circular plates. Thedimensions of plates 124 and 126 may be larger than the dimensions ofwafer 110, such that the surface area of wafer 110 can be completelyoverlaid by the surface area of heating plates 124 and 126. In oneexample, the circular diameters of heating plates 124 and 126 is greaterthan the diameter of wafer 110. For example, as illustrated in FIG. 4A,the radius of bottom heating plate 126 is greater than the radius ofwafer 110 by about a length γ, which can range between about 1 mm and100 mm, preferably 25-to-50 mm.

[0030] For convenience of understanding, FIG. 4A illustrates anembodiment of a heatable member, for example, top plate 124. It shouldbe understood that top plate 124 is similar in structure and function tobottom plate 126, and the description of top plate 124 is the same asfor bottom plate 126, unless otherwise noted. In accordance with oneembodiment of the present invention, on a periphery of heating top plate124 is at least one heat source 222. Heat source 222 may be a resistiveheating element or other conductive heat source, which can be made tocontact a peripheral portion of top heating plate 124 or may be embeddedwithin top heating plate 124. The resistive heating element may be madeof any high temperature rated material, such as a suitable resistivelyheatable wire, which is made from a high mass material for increasedthermal response and high temperature stability, such as SiC, SiC coatedgraphite, graphite, AlCr, AlNi and other alloys. Resistive heatingelements of this type are available from Omega Corp. of Stamford, Conn.Alternatively, top heating plate 124 can be heated using a radiantsource.

[0031] In one embodiment, plates 124 and 126 may be positioned suspendedwithin process chamber 106, in a cantilevered relationship on a wall ofthe process chamber. In this embodiment, coupling mechanism 224 includesa mounting bracket 228 and electrical leads 230 to provide an electricalpower connection to heat source 222. Mounting bracket 228 can be coupledto an internal wall of process chamber 106 using conventional mountingtechniques. Once mounted, electrical leads 230 can extend outside ofprocess chamber 106 to be connected to an appropriate power source. Thepower source may be a direct line voltage of between about 100 volts andabout 500 volts. Alternatively, top plate 124 may hang suspended frommounts emanating down from a ceiling of process chamber 106 and bottomplate 126 may rest on mounts emanating up from a floor of processchamber 106.

[0032]FIG. 4B is a simplified cross sectional view of heating plate124,126, in accordance with the present invention. Heating plates 124, 126can include a hollowed out portion defining an internal cavity 250.Internal cavity 250 has an inlet 252, which enters internal cavity 250on a first side 256 of plate 124, 126. Inlet 252 allows a gas to be fedfrom a gas reservoir (not shown) into internal cavity 250. The gas mayinclude, for example, any suitable gas, such as He, H₂, O₂, Ar, N₂ andthe like.

[0033] Internal cavity 250 has an outlet portion 254, which is definedon a second side 258 of plate124, 126. Outlet portion 254 allows the gasthat has entered internal cavity 250 to escape the cavity. In oneembodiment, outlet portion 254 can be defined as a plurality of outletsor holes 255. Holes 255 can be any suitable size that allow passage ofthe gas. In one example, holes 255 may be between about 0.1 mm to about2 mm in diameter.

[0034] In one embodiment, internal cavity 250 may include a baffle 260,positioned between inlet 252 and outlets 255. In this embodiment, baffle260 impedes the flow of the gas entering through inlet 252. By impedingthe otherwise forced gas flow before exiting through outlets 255, thegas is made to reside in internal cavity 250 for a longer time period,which allows more heat to be transferred to the gas before the gas exitsthe cavity.

[0035] In one embodiment, the thickness of top and bottom plates 124 and126 is any thickness d suitable for accommodating heat source 222 andfor providing an adequately sized internal cavity 250. The thickness dcan range from between 1 cm and 10 cm; preferably about 3 cm. In oneexample, plates 124 and 126 can be fabricated using a splitconstruction, which means that each plate is originally two pieces 263and 267, joined at seam 265, for example, by welding. Baffle 260 can bemounted onto piece 267, for example, using attaching device 261, such asscrews, nuts and bolts, rivets and the like and a spacer 269. It shouldbe noted that one of ordinary skill in the art may fabricate plates 124and 126 using a variety of well known techniques, all of which fallwithin the scope of the present invention. Generally, plates 124 and 126may be made of materials, such as Al, and Al alloys Ni, Inconel, Mo,stainless steel, SiC and the like.

[0036] Referring now to FIGS. 4B, 5 and 6, in operation, internal cavity250 serves as a heat exchanger, such that the gas can be heated as ittravels from inlet 252 through to the exit points of outlets 254. Theentering gas can be at ambient temperature or may be pre-heated prior toentering internal cavity 250. The gas is made to move through internalcavity 250 which may be heated by heat source 222 to betweenapproximately 100° C. and 1000° C. It should be understood that thetemperature of the gas exiting internal cavity 250 depends on, forexample, the type of gas, the flow rate of the gas, the residence timeof the gas in internal cavity 250 and the nominal temperature ofinternal cavity 250. Each of these parameters can be adjusted until theexiting gas temperature is appropriate for a specific process.

[0037] As shown in FIG. 5, in one embodiment, wafer 110 is placedbetween top and bottom plates 124 and 126 and a gas, such as N₂, isallowed to flow through internal cavity 250 of top plate 124. In thisexample, the gas enters internal cavity 250 at approximately roomtemperature (25° C.). The gas is heated by radiation and conduction asit passes through cavity 250 and exits outlets 255.

[0038]FIG. 6 is a graph showing an exemplary result of a heating processusing the configuration of FIG. 5. In this example, heat source 222 isset to about 220° C., which causes the gas to exit outlets 255 atapproximately 215° C.

[0039] As illustrated by line 264 in FIG. 6, allowing gas to flowthrough top plate 124 only, wafer 110 reaches the temperature ofapproximately 220° C. in about 60 seconds. Line 266 illustratesapproximately the same heating profile if gas is allowed tosimultaneously flow through bottom plate 126. For comparison, line 262represents the heating profile of wafer 110 without gas flow througheither top plate 124 or bottom plate 126. As illustrated by line 262,approximately 270 seconds are required to first heat wafer 110 toapproximately 210° C.

[0040]FIG. 7 is a simplified illustration of another embodiment inaccordance with the present invention. In this embodiment, processchamber 106 is structurally the same as in other embodiments, includingtop plate 124 and bottom plate 126. However, instead of heating the gasas it enters chamber 106, gas is removed from chamber 106, through topplate 124 and bottom plate 126 to provide forced convection cooling ofwafer 110. In operation, when cooling is desired, a vacuum is pulledthrough inlets 252 to cause gas to flow out from chamber 106 in adirection generally indicated by air flow arrows 270 and into outlets255. In this embodiment, outlet portion 254 becomes an inlet to internalcavity 250 and gas inlet 252 provides an outlet for internal cavity 250.

[0041] In one embodiment, an exhaust port 272 in chamber 106 can beopened to provide ambient air for cooling. As the ambient air is movedover the surface of wafer 110, the wafer surface is cooled. In oneembodiment, the cooling rate can range from between approximately 5°C./sec and 20° C./s.

[0042]FIG. 8 shows another embodiment for moving gas over the surface ofwafer 110. In this embodiment, a gas inlet 280 is positioned on chamber106 approximately in-line and parallel to wafer 110. An outlet orexhaust port 282 is also positioned in-line and parallel to wafer 110,and approximately in-line with inlet 280. In operation as a gas isallowed into chamber 106 through inlet 280, outlet port 282 , undervacuum, causes the gas to flow over wafer 110 providing a forceconvection cooling effect.

[0043] Having thus described embodiments of the present invention,persons skilled in the art will recognize that changes may be made inform and detail without departing from the spirit and scope of theinvention. Thus the invention is limited only by the following claims.

What is claimed is:
 1. A system for processing a semiconductor device,the system comprising: a processing chamber; and a first platepositioned within said processing chamber and defining a first internalcavity configured to receive a first gas through a first passage intosaid first internal cavity at a first temperature and to emit said firstgas from said first internal cavity at a second temperature through asecond passage.
 2. The system of claim 1, further comprising a secondplate disposed adjacent to said first plate, wherein said second platedefines a second internal cavity configured to receive a second gasthrough a first passage into said second internal cavity at a firsttemperature and to emit said gas from said second internal cavity at asecond temperature through a second passage.
 3. The system of claim 2,wherein said second passages comprise a plurality of holes defined on asurface of said first and said second plates.
 4. The system of claim 2,wherein said first plate and said second plate comprises a heat sourcefor heating said plate to a preselected temperature.
 5. The system ofclaim 1, wherein said first gas is taken from the group consisting ofN₂, He, H₂, O₂, Ar and gas mixtures containing He, H₂, O₂, Ar and N₂. 6.The system of claim 1, wherein said internal cavity further comprises abuffer to disperse said first gas throughout said internal cavity.
 7. Asystem for wafer processing comprising: a chamber; and at least oneheatable plate positionable within said chamber, including: an internalcavity defining an internal wall and configured to receive a gas; meansfor heating said internal wall to a preselected temperature; and anoutlet portion defining a plurality of holes for emitting said gas. 8.The system of claim 7, wherein said at least one heatable platecomprises a first heatable plate and a second heatable plate disposedhaving adjacent surfaces configured to receive a wafer therebetween. 9.The system of claim 7, wherein said gas is taken from the groupconsisting of He, H₂, O₂, Ar, N₂ and gas mixtures containing He, H₂, O₂,Ar, and N₂.
 10. The system of claim 7, wherein said internal cavityfurther comprises a buffer to disperse said first gas throughout saidinternal cavity.
 11. A method for processing a semiconductor device, themethod comprising: providing a first heatable member including: aninternal cavity defining an internal wall; means for heating saidinternal wall to a preselected temperature; and an outlet portiondefining a plurality of holes; introducing a gas into said internalcavity of said first heatable member; heating said gas substantially tosaid preselected temperature; and impinging a surface of a semiconductorwafer with said heated gas to change the temperature of saidsemiconductor wafer.
 12. The method of claim 11, wherein heating saidgas substantially to said preselected temperature comprises heating saidinternal wall with a resistance heating element to said preselectedtemperature.